OK, let's work through this together. We're starting with 885 and we're going to multiply it by 91, which means we add 885 to itself 91 times.
Step 1: 0 + 885 = 885
Step 2: 885 + 885 = 1770
Step 3: 1770 + 885 = 2655
Step 4: 2655 + 885 = 3540
Step 5: 3540 + 885 = 4425
Step 6: 4425 + 885 = 5310
Step 7: 5310 + 885 = 6195
Step 8: 6195 + 885 = 7080
Step 9: 7080 + 885 = 7965
Step 10: 7965 + 885 = 8850
Step 11: 8850 + 885 = 9735
Step 12: 9735 + 885 = 10620
Step 13: 10620 + 885 = 11505
Step 14: 11505 + 885 = 12390
Step 15: 12390 + 885 = 13275
Step 16: 13275 + 885 = 14160
Step 17: 14160 + 885 = 15045
Step 18: 15045 + 885 = 15930
Step 19: 15930 + 885 = 16815
Step 20: 16815 + 885 = 17700
Step 21: 17700 + 885 = 18585
Step 22: 18585 + 885 = 19470
Step 23: 19470 + 885 = 20355
Step 24: 20355 + 885 = 21240
Step 25: 21240 + 885 = 22125
Step 26: 22125 + 885 = 23010
Step 27: 23010 + 885 = 23895
Step 28: 23895 + 885 = 24780
Step 29: 24780 + 885 = 25665
Step 30: 25665 + 885 = 26550
Step 31: 26550 + 885 = 27435
Step 32: 27435 + 885 = 28320
Step 33: 28320 + 885 = 29205
Step 34: 29205 + 885 = 30090
Step 35: 30090 + 885 = 30975
Step 36: 30975 + 885 = 31860
Step 37: 31860 + 885 = 32745
Step 38: 32745 + 885 = 33630
Step 39: 33630 + 885 = 34515
Step 40: 34515 + 885 = 35400
Step 41: 35400 + 885 = 36285
Step 42: 36285 + 885 = 37170
Step 43: 37170 + 885 = 38055
Step 44: 38055 + 885 = 38940
Step 45: 38940 + 885 = 39825
Step 46: 39825 + 885 = 40710
Step 47: 40710 + 885 = 41595
Step 48: 41595 + 885 = 42480
Step 49: 42480 + 885 = 43365
Step 50: 43365 + 885 = 44250
Step 51: 44250 + 885 = 45135
Step 52: 45135 + 885 = 46020
Step 53: 46020 + 885 = 46905
Step 54: 46905 + 885 = 47790
Step 55: 47790 + 885 = 48675
Step 56: 48675 + 885 = 49560
Step 57: 49560 + 885 = 50445
Step 58: 50445 + 885 = 51330
Step 59: 51330 + 885 = 52215
Step 60: 52215 + 885 = 53100
Step 61: 53100 + 885 = 53985
Step 62: 53985 + 885 = 54870
Step 63: 54870 + 885 = 55755
Step 64: 55755 + 885 = 56640
Step 65: 56640 + 885 = 57525
Step 66: 57525 + 885 = 58410
Step 67: 58410 + 885 = 59295
Step 68: 59295 + 885 = 60180
Step 69: 60180 + 885 = 61065
Step 70: 61065 + 885 = 61950
Step 71: 61950 + 885 = 62835
Step 72: 62835 + 885 = 63720
Step 73: 63720 + 885 = 64605
Step 74: 64605 + 885 = 65490
Step 75: 65490 + 885 = 66375
Step 76: 66375 + 885 = 67260
Step 77: 67260 + 885 = 68145
Step 78: 68145 + 885 = 69030
Step 79: 69030 + 885 = 69915
Step 80: 69915 + 885 = 70800
Step 81: 70800 + 885 = 71685
Step 82: 71685 + 885 = 72570
Step 83: 72570 + 885 = 73455
Step 84: 73455 + 885 = 74340
Step 85: 74340 + 885 = 75225
Step 86: 75225 + 885 = 76110
Step 87: 76110 + 885 = 76995
Step 88: 76995 + 885 = 77880
Step 89: 77880 + 885 = 78765
Step 90: 78765 + 885 = 79650
Step 91: 79650 + 885 = 80535

So, 885*91 = 80535